This invention generally relates to packaging of semiconductor modules. More particularly, it relates to a semiconductor package that has a large number of connections. Even more particularly, it relates to a semiconductor package able to accommodate a large number of connections with improved electrical characteristics.
High pin count semiconductor packages, such as high density ball grid array or column grid array surface mount packages, require more complicated and expensive printed circuit (PC) boards to accommodate the large number of connections. In one alternative, each ball or pin connector on the semiconductor package can be shrunk and spaces between balls and pins can be reduced as well. However, to accommodate the larger number of connections more layers of metal must be provided in the PC board. In addition the smaller contacts increase series resistance and closer contacts increase capacitance, and the two effects combine to increase RC delay, degrading performance. Also there is a greater likelihood of bridging across closer contacts.
In a second alternative, higher pin count can be accomplished by providing larger semiconductor packages, with the wiring spread out in the package. But larger packages add to package cost, reduce performance from longer leads in the package, and use up more valuable real estate on the PC board. In addition, larger packages suffer more from thermal expansion mismatch, and therefore offer lower reliability. Thus, a better solution for high pin count semiconductor packages is needed that avoids larger packages, lower reliability, extra levels of metal in PC boards, degraded electrical performance, and closer contacts, and this solution is provided by the following invention.
It is therefore an object of the present invention to increase the number of connections to a package by providing an area array of connections on more than one surface of the package.
It is a further object of the present invention to provide a system comprising a pair of printed circuit boards connected to a single semiconductor package.
It is a feature of the present invention that the package has an area array of connectors on two or more surfaces.
It is a further feature of the present invention that the package has the area array of connections on top and bottom surfaces.
It is an advantage of the present invention that the number of connections to a package is substantially higher without decreasing the size of connectors or the space there between, and without increasing the size of the package, the length of leads, or RC delay.
It is an advantage of the present invention that the number of connections to a package is substantially higher without degrading electrical characteristics.
These and other objects, features, and advantages of the invention are accomplished by a substrate for electrical and mechanical connection to a semiconductor chip. The substrate includes a top surface and a bottom surface. A first area array of contacts is on the top surface and a second area array of contacts is on the bottom surface. The first array is for connecting the module to a first carrier and the second array is for connecting the module to a second carrier. At least one contact of the first array is not connected to a contact of the second array through the substrate.
Another aspect of the invention is accomplished by a semiconductor module, that includes a chip having a first chip contact and a second chip contact. A substrate is electrically and mechanically connected to the chip. The substrate has a first surface and a second surface different from the first surface. The substrate further comprises a first substrate contact on the first surface and a second substrate contact on the second surface. The first chip contact is electrically connected to the first substrate contact and the second chip contact is electrically connected to the second substrate contact. The first substrate contact does not connect with the second substrate contact through the substrate.